Identification and Characterization of Genes that Control the Phenolic

We isolated a cDNA clone for grape 4-coumaryl-CoA ligase (4CL) which is nearly full length. This is an enzyme that is positioned at an important branch-point in phenolic metabolism. We inserted the partial cDNA clone into an expression system, and initial experiments indicate that we can obtain sufficient quantities of purified grape 4CL for antibody production. We also inserted a 4CL clones from poplar into an E.coli expression system and demonstrated that permeabilized cells containing poplar 4CL are able to produce caffeoyl-CoA. Although the yield of caffeoyl-CoA is lower than we had hoped, it will be more than adequate for use in the assay of tartrate O-hydroxycinnamoyltransferase from grape. We isolated cDNA clones for grape dihydroflavonol reductase and a glucosyl transferase. The glucosyl transferase may be involved in glycosylation of phenolic compounds in grape, such as glycosylation of anthocyanidins to give the anthocyanins found in the hypodermal cells of the berry skin. The substrate specificity of the glucosyl transferase has not been determined, thus its exact role in phenolic biosynthesis has not been confirmed. The dihydroflavonol reductase is important because the product of the reaction (flavan-3,4-diols )can be directed into several different classes of phenolics in grape berries such as catechin, epicatechin, tannins and anthocyanins. Like the 4CL enzyme described above, the dihydroflavonon reductase occurs at an important branch point in phenolic metabolism in grape.